1. Field of the Invention
This invention relates to an improvement in a press die set, and an improvement in a press machine for driving it.
2. Disclosure of the Prior Art
A press die set, as shown in FIG. 14, has two thick plates, one at the top and the other at the bottom. The upper plate (punch holder) is mounted with a cylindrical guide bush 31. The lower plate (die holder) is mounted with a columnar guide post 33. A retainer 32 is cylindrical, through which the guide post 33 passes, and on the outer side of which the guide bush 31 contacts. The guide bush 31, the retainer 32, and the guide post 33 guidesmoothvertical sliding of the upper plate (punch holder) while maintaining a parallel relationship with the lower plate (die holder).
Conventionally, a ball retainer as shown in the figure has been widely used as the retainer. The ball retainer 70 rotatably holds a number of ball bearings 702 in a substantially cylindrical plastic case 701. The thickness of the case 701 is made smaller than the diameter of ball bearings 702 so that the ball bearings are caused to pass through the inside of the case, and contact the guide post, but the case does not contact the guide post. Similarly, the ball bearings contact the guide bush which surrounds and slides around the outside of the ball retainer. Then, as the ball bearings rotate, the guide post, the ball retainer, and the guide bush mutually slide.
A conventional guide post is a column the outer diameter of which is slightly smaller than the inner diameter of the retainer. In addition, a conventional guide bush is a cylinder the inner diameter of which is slightly larger than the outer diameter of the retainer. Lubricant such as grease is applied between the ball bearings and the guide post or the guide bush for a smooth sliding motion.
In addition, as shown in FIG. 2, components relating to a stripper are mounted near the center of each plate. The upper plate (punch holder) is mounted with a columnar stripper guide pin 35 with a small diameter. The lower plate (die holder) is mounted with a cylindrical die guide bush 36. A planar stripper 39 is mounted with a cylindrical stripper guide bush 34, and a hole at its center through which the blade of a trimming punch 37 passes. A substantially cylindrical trimming die button 38 with a recess of a small diameter is mounted at the center of a plate mounted in parallel to the lower plate. The stripper guide bush 34 of the stripper 39 is inserted through near the center of the stripper guide pin 35 the end of which the die guide bush 36 mounted on the lower plate passes through.
A manner to stamp a plate work by using the above press die set will be described. The hole in the top surface of the trimming die button 38 has a substantially same shape as the trimming punch 37, but slightly larger in its size to provide a gap or clearance. A hole with a shape and size determined by the dimensions of the trimming punch 37 and the trimming die button 38 is formed in the work by placing it on the trimming die button 38, and lowering the trimming punch 37.
A conventional press machine for driving the press die set will be described. As shown in FIG. 1, a planar bolster is placed across the receiver of a press machine, and a die holder is mounted on the bolster. The die holder is also planar. There is a planar ram over the press machine. The ram vertically slides, and a bearing is interposed between the end plate of the ram and the frame of the press machine. A punch holder is mounted under the ram. The punch holder is also planar. Conventionally, all of the bolster, the die holder, the punch holder, and the ram are of casting iron or iron-base alloy. The receiver of the press machine horizontally and inwardly projects from the frame. That is, a large space is formed at the center.